1. Field of the Invention
The present invention relates to a method of manufacturing a contact of a semiconductor device using apparatus having a plasma pretreatment module. More particularly, the present invention relates to pretreatment processes from the time a contact hole is formed using a photoresist pattern to the time material is deposited in the contact hole.
2. Description of the Related Art
A highly integrated semiconductor device is produced by stacking numerous conductive or semiconductor layers one atop the other with respective insulating layers interposed therebetween, and connecting the conductive or semiconductor layers to one another. Typically, a contact hole is used to electrically connect the conductive layers or semiconductor layers. A method of forming such a highly integrated semiconductor device includes steps of forming a lower (conductive or semiconductor) layer, forming an insulating layer thereon, forming a contact hole through the insulating layer and which contact hole exposes the lower layer, and forming an upper (conductive or semiconductor) layer on the insulating layer that fills the contact hole with conductive material.
In general, the contact hole is formed by a plasma dry etching process. In this process, the insulating layer is etched by reactive ions of plasma moving at high speeds. Because manufacturing a semiconductor device almost always involves anisotropic etching, the plasma dry etching process is one of the essential processes in the manufacturing of semiconductor devices.
However, when plasma dry etching is carried out, reactive ions of the plasma create a lattice defect on the surface of the wafer or damage the surface that becomes exposed at the bottom of the contact hole. If allowed to exist, such a defect or damage would adversely affect the electrical characteristics of the device.
Accordingly, conventional treatment processes include a process of annealing the wafer to prevent the surface thereof from being damaged during the plasma etching process, and a plug implantation process after the contact hole is formed to correct for any damage at the surface defining the bottom of the contact hole. Also, there is known a process of removing the damaged layer at the bottom of the contact hole.
FIG. 1 shows a conventional manufacturing method from the time a contact hole is formed to the time an upper conductive or semiconductor layer is formed. Referring to FIG. 1, the contact hole is formed by a plasma dry etching apparatus (S10). In general, the contact hole is formed by forming an insulating layer on a semiconductor substrate or other specific underlayer (or xe2x80x9cbottom layerxe2x80x9d), forming a photoresist pattern on the insulating layer using a photolithographic technique, and etching the insulating layer using the photoresist pattern as an etching mask.
Next, the semiconductor substrate is moved to an ashing apparatus, whereupon the photoresist pattern is ashed and removed (S12). Next, a photoresist (PR) strip process is performed (S14). In this process, the semiconductor substrate is transferred from the ashing apparatus to a wet tub filled with sulfuric acid to remove remnants of the photoresist pattern that were not removed by the ashing process.
Next, a residue processing process is performed to remove a damaged layer formed by the plasma dry etching process at the surface of the semiconductor substrate or at the surface of the specific underlayer defining the bottom of the contact hole (S16). The residue processing process is performed using a low bias condition and CF4 or oxygen gas. Next, a pretreatment cleaning process is performed in the wet tub (S18) to remove another damaged layer formed by the residue processing process and to remove any remaining contaminants, such as carbon, from the contact hole.
Subsequently, the pre-processed semiconductor substrate is transferred to a deposition apparatus, whereupon the upper layer is formed to fill the contact hole (S20).
However, the conventional manufacturing method is subject to the following problems.
First, the photoresist (PR) strip process requires significant processing time and increases the probability that the semiconductor substrate will be contaminated because the PR strip process is performed in a wet tub filled with sulfuric acid.
Second, the surface exposed by the contact hole can be damaged by the residue processing process performed by the dry etching apparatus. However, even though the damaged layer can be removed by performing a pre-treatment cleaning process in a wet tub, the etch rates of various layers defining the side walls of the contact hole vary with respect to the cleaning solution used in the pretreatment cleaning process. Thus, the side walls defining the contact hole become uneven and the pattern formed on the semiconductor substrate deteriorates due to over-etching.
Third, even after the pretreatment cleaning process is performed, a new natural oxide film is formed on the surface defining the bottom of the contact hole as the semiconductor substrate is transferred to the deposition apparatus. The natural oxide film prevents a good contact from being established between the surface of the lower layer defining the bottom of the contact hole and the upper layer formed by the deposition process.
Fourth, it is difficult to integrate the processes because the dry etching and deposition processes are generally performed on one wafer at a time, whereas the photoresist PR strip process and the pretreatment cleaning process featuring the use of a wet tub are batch processes. Accordingly, the semiconductor substrates must be transferred through separate processing apparatus, whereby the substrate are more apt to become contaminated. Therefore, although a great deal of processing time is spent, many of the devices still will have inferior electrical characteristics.
An object of the present invention is to solve the above-described problems of the prior art.
More specifically, an object of the present invention is to provide a method of forming a contact of a semiconductor device in which the pretreatment processes necessary for forming a good contact can be performed in a relatively short time.
Another object of the present invention is to provide a method of forming a contact of a semiconductor device in which the pretreatment processes necessary for forming a good contact are performed without the semiconductor substrate being contaminated in the interim between processes.
To achieve these objects, the present invention provides a method in which the pretreatment processes, from the time the contact hole is formed to the time the contact hole is filled, are carried out using plasma.
The contact hole is formed using a photoresist pattern as an etching mask, wherein the surface of an underlying material comprising silicon is exposed. Subsequently, the semiconductor substrate is loaded into a clustered apparatus having one or more plasma pretreatment and deposition modules connected to each other through means in which a vacuum can be maintained. In a first pretreatment process, the photoresist pattern is removed by ashing. In a second pretreatment process, a damaged layer at the surface exposed by the contact hole is removed. In a third pretreatment process, the semiconductor substrate is cleaned. The semiconductor substrate is then transferred to the deposition module while the substrate is kept in a vacuum. There, a film is formed on the substrate to fill the contact hole and thereby establish electrical contact with the underlayer.
The underlayer can be a silicon, polysilicon, or silicide layer. The upper layer formed to fill the contact hole is a conductive film such as one formed of a polysilicon layer and a metal layer.
The plasma pretreatment module is designed to generate remote plasma using microwaves. In this respect, the process of ashing the photoresist pattern is performed using nitrogen gas and oxygen gas in a plasma state, followed by an application of UV light. The process of removing the damaged layer is performed using nitrogen gas and oxygen gas in a plasma state and a fluorine-based gas in a plasma state or in a normal gaseous state. And, the cleaning process comprises using hydrogen gas and a fluorine-based gas in a plasma state to cause a chemical reaction with an oxide layer on the surface of the underlayer exposed at the bottom of the contact hole, thereby forming a reaction layer, and annealing the reaction layer vaporize the same.
According to the present invention, an ashing process, a residue processing process, and a pretreatment cleaning process may be continuously performed in a plasma pretreatment module of a clustered apparatus. Thus, the pretreatment processing time can be minimized. Also, contaminants are prevented from accumulating in the contact hole in contrast to the case in which the semiconductor substrate is transferred among the various processing apparatus of the prior art.
In addition, the deposited material and the surface exposed by the contact hole contact each other well because a vacuum is maintained between the plasma pretreatment module and the deposition module to prevent a natural oxide film from being grown on the exposed surface after the pretreatment cleaning process is performed.